The recovery of hydrocarbons, especially oil, frequently involves the injection of fluids into the reservoir to either force or drive the hydrocarbons from one location to another, as in flooding operations, or even more basically stated, to improve the flow of the hydrocarbons to the production well as in various stimulation operations. Carbon dioxide and other fluids, including water and steam, are frequently injected for such purposes, particularly for the recovery of oil.
In enhanced oil recovery using CO.sub.2 flooding, the channeling and gravity override of injected CO.sub.2 are common problems. Channeling is due to high permeability zones or "thief" zones which exist in the reservoir or due to the high mobility ratio of CO.sub.2 to oil. The override effect is due to the density difference between CO.sub.2 and the oil. Early CO.sub.2 breakthrough can occur if either of these conditions exists, leading to bypassing of a considerable volume of the oil in the reservoir.
To correct the channeling and the override problems, polymer gels may be used to reduce the permeability or to plug off these areas. The major difficulty of some of the polymer gel processes is the lack of selectivity of the treatment. Placing polymer gels in the wrong areas will not solve the problem and can even damage the reservoir. Mechanical packers are sometimes used to isolate the zones to be treated, but such a process is tedious and expensive.
Therefore, what is needed is a stable gel which can form in situ in a low pH environment and selectively close a carbon dioxide overswept zone where oil is more depleted.